SEO is a complex topic, and there are many factors that impact it. For the Google search engine, PageRank is one of those factors.

PageRank is basically a computer algorithm for determining how important a page is on the internet. It is calculated based upon the number of pages that link to your page, as well as the PageRank of those pages. So for example, getting the front page of cnn.com to link to your page will increase your PageRank more than putting a link on your neighbor's blog.

Companies that specialize in SEO can provide a little assistance here, if you're willing to pay for it. They can get your link on pages known to have a high PageRank. However, this usually isn't the best use of your money. The best bang for your buck you can get from SEO companies is advice on how to structure your content in such a way that it will be indexed the way you want it. From there, it's up to you to provide content that is interesting enough that other people will want to link to it.

SEO in my experience comes down to primarily three things.

1. Good content - meaning it is original and highly informative, has appropriate titles, is well organized etc.
2. Good html and other technical implementation including ways to make spidering easier.
3. Solid links from other sites - meaning not link farms and not obviously placed links that are intended solely to drive up page rank.

There are other factors too - but these I think are the primary ones.

Wikipedia has a pretty good explanation of how PageRank works. Here's a summary from Google's site:

PageRank relies on the uniquely democratic nature of the web by using its vast link structure as an indicator of an individual page's value. In essence, Google interprets a link from page A to page B as a vote, by page A, for page B. But, Google looks at more than the sheer volume of votes, or links a page receives; it also analyzes the page that casts the vote. Votes cast by pages that are themselves "important" weigh more heavily and help to make other pages "important".

Jerry,

I answer a question very similar to this here:
http://startups.com/questions/2152/how-can-a-site-gain-presence-in-google/2212#2212

And basically what it comes down to is:

        Make something great. Tell people about it. Do it again.

You want to have relevant, continually updated content that provides value to your target audience and is frequently linked to and talked about in other places on the web. That's it. There are lots of little tricks you can find if you search for SEO, but that's all they is tricks. If all your competitors do the same searches and find the same tricks and use them, your content is the only thing that differentiates you. Providing useful information that people talk about will move you up the rankings, eventually. There are no shortcuts though.

HTH,
Randall